I understand your question here are some reason it isn't a problem to keep as many fish as we do.
Rend lake is a crappie factory! It has 160+ miles of shoreline and over half those miles are covered in buck brush. Buck brush makes perfect spawning habitat and then makes perfect a nursery for fry after they hatch.
The limit on rend ( 25 fish total with only 10 over 10" per person) has helped the quality of fish in the lake but there's never been a problem of not enough fish. Crappie will actually stunt themselves in any body of water without heavy fishing pressure so it's actually good to keep tons of crappie. To also help put things in perspective on average my uncle and I clean approximately 10,000 a year out of rend, that breaks down to .52 fish per acre that's less than 1 fish an acre per year.
If you have any other questions feel free to ask.